Download Composting: A Guide to Managing Organic Yard Wastes

C O M P O S T I N G
A Guide to Managing Organic
Yard Wastes
America’s waste disposal sites are filling up.
Landfills across the nation are being closed at
an alarming rate. Yet the volume of waste our
society produces continues to increase.
Twenty percent of the solid waste placed in
landfills consists of yard and garden wastes
such as leaves and grass clippings. Many
states, including North Carolina, are banning
these wastes from landfills.
One step we can take toward solving our
waste disposal problems is to make use of lawn
and garden wastes instead of dumping them.
Through the process of composting, these organic wastes can be recycled to produce a natural material that can be
used in gardens, landscapes, and flower beds.
When mixed with soil, compost increases the organic matter content,
improves the physical properties of the soil, and supplies essential nutrients, enhancing the soil’s ability to support plant growth. Compost can
also be applied to the soil surface to conserve moisture, control weeds,
reduce erosion, improve appearance, and keep the soil from gaining or
losing heat too rapidly.
One way to dispose of yard and garden wastes is to haul them to municipal or county composting facilities. Many homeowners, however, find
it more convenient and economical to compost these materials in their own
backyards. In either case, the finished compost can be mixed with soil or
used as a mulch for gardens, landscape beds, or lawns. This publication
explains how to build and maintain a compost pile and how to use compost
in the yard and garden.
Why Compost?
Gardeners have used compost for centuries. Composting is an efficient method of breaking down
organic materials into an end product that is beneficial to soil and plants. Adding yard and garden
wastes directly to the soil without first composting
them has some undesirable effects. For example, if
large quantities of uncomposted leaves are incorporated into the soil, the microbes that work to decompose the leaves will compete with plant roots for soil
nitrogen. This competition can result in nitrogen
deficiency and poor plant growth. Increased populations of the microbes can also deplete most of the
organic matter in the soil, leaving the soil with less
structure than before.
When materials such as leaves and grass clippings
are composted, however, a microbial process
converts them to a more usable organic material.
Adding composted material reduces the competition
for nitrogen. Composted material is also much easier
to handle and mix with soil than uncomposted
material because of its finer texture. Furthermore,
improvement of the soil’s physical properties — such
as increased infiltration, better drainage, and greater
water holding capacity — usually occurs more
rapidly when composted materials are added.
Requirements for Efficient Decomposition
Decomposition of organic material in a compost pile
depends on maintaining the activity of decomposer
microbes. Any factor that slows or halts the growth
of these microbes also slows the composting process.
Efficient decomposition occurs when aeration and
moisture are adequate, when the particles of waste
material are small, and when the proper amounts of
fertilizer and lime are added. We will discuss each of
these factors in more detail.
AERATION
Microbes require oxygen to decompose organic
wastes efficiently. Some decomposition will occur in
the absence of oxygen (that is, under anaerobic
conditions); however, the process is slow and foul
odors may develop. Because of the odor problem,
composting without oxygen is not recommended in
residential areas unless the process is conducted in a
fully closed system (such as the plastic bag method
described later under “Composting Structures”).
Mixing the pile once or twice a month will provide
the necessary oxygen and significantly hasten the
composting process. A pile that is not mixed may
take three to four times longer to produce useful
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compost. A well-mixed compost pile also reaches
higher temperatures, helping to destroy weed seeds
and disease-causing organisms (pathogens).
MOISTURE
Adequate moisture is essential for microbial activity.
Materials in a dry compost pile will not decompose
efficiently. If rainfall is limited, the pile must be
watered periodically to maintain a steady decomposition rate. Enough water should be added to completely moisten the pile, but overwatering should be
avoided. Excessive moisture can lead to anaerobic
conditions, slowing down the degradation process
and causing foul odors. The pile should be watered
enough that it is damp but does not remain soggy.
Approximately 50 to 55 percent moisture on a weight
basis is a good starting point. The compost is within
the right moisture range if a few drops of water can
be squeezed from a handful of material. If no water
can be squeezed out, the materials are too dry. If
water gushes out, they are too wet.
PARTICLE SIZE
The smaller the organic waste, the faster the compost
will be ready to use. Smaller particles have much
more surface area for a given volume and thus are
more rapidly broken down by microbes. Materials
can be shredded before they are added to the pile.
Shredding is essential if brush or sticks are to be
composted. In addition to speeding up the composting process, shredding reduces the volume of the
compost pile. A low-cost method of reducing the
size of fallen tree leaves is to mow the lawn before
raking it or to run the lawn mower over leaf piles
after raking. Raked piles should be checked to
ensure that they do not contain sticks or rocks that
could cause injury during mowing. If the mower has
an appropriate bag attachment, the shredded leaves
can be collected directly.
FERTILIZER AND LIME
Microbial activity is affected by the ratio of carbon to
nitrogen in the organic waste. Because microbes
require a certain amount of nitrogen to live and grow,
a shortage of nitrogen slows the composting process
considerably. Materials high in carbon but low in
nitrogen, such as straw or sawdust, decompose very
slowly unless nitrogen fertilizer is added. Although
tree leaves are higher in nitrogen than straw or
sawdust, they still decompose more rapidly when
nitrogen fertilizer or wastes that are high in nitrogen
are added. Grass clippings are generally high in
nitrogen; when mixed properly with leaves, they
speed decomposition. Poultry litter, manure, or
blood meal can be used as organic sources of
nitrogen. Otherwise, a fertilizer with a high nitrogen
analysis (10 to 30 percent) should be used. Other
nutrients such as phosphorus and potassium are
usually present in adequate amounts.
During the initial stages of decomposition, organic
acids are produced and the acidity (pH) of the
compost drops. At one time it was believed that
adding small amounts of lime in the early stages
would maintain and enhance microbial activity during
this period. However, lime converts ammoniumnitrogen to ammonia gas, removing nitrogen from the
pile. Although adding lime may hasten decomposition, the loss of nitrogen from the pile often offsets
the benefits. Lime is not necessary for degradation
of most yard wastes. Finished compost is usually
alkaline (with a pH between 7.1 and 7.5) without the
addition of lime. In many areas, the water used to
moisten the compost pile is alkaline and may also
help to raise the pH (reduce the acidity) of the
compost. If large quantities of pine needles, pine
bark, or vegetable and fruit wastes are composted,
additional lime may be necessary to reduce acidity.
Materials for Composting
Many organic materials are suitable for composting.
Yard wastes such as leaves, grass clippings, straw,
and nonwoody plant trimmings can be composted.
Leaves are the dominant organic waste in most
backyard compost piles. Grass clippings can be
composted; however, with proper lawn management,
clippings do not need to be removed from the lawn.
If allowed to remain, they will decay and release
nutrients, reducing the need for fertilizer. (See
Cooperative Extension Service publication AG-69,
Carolina Lawns.) If clippings are used, they should
be mixed with other yard wastes; otherwise they may
compact and restrict airflow. Branches and twigs
greater than 1/4 inch in diameter should be put
through a shredder or chipper first. Kitchen wastes
such as vegetable scraps, coffee grounds, and
eggshells may also be added.
Sawdust may be added in moderate amounts if
additional nitrogen is applied. Approximately 1 pound
of actual nitrogen (6 cups of ammonium nitrate) is
required per hundred pounds of dry sawdust. Wood
ashes serve as a lime source; if used, they should be
added only in small amounts (no more than 1 cup per
bushel or 10 pounds per ton of compost). Excessive
amounts result in loss of nitrogen from the pile.
However, wood ashes do contribute high levels of
potassium to the compost. Crushed clam or oyster
shells, eggshells, and bone meal also tend to reduce
the acidity of composts. Ordinary black-and-white
newspaper can be composted; however, the nitrogen
content is low, slowing the decomposition rate. If
paper is composted, it should make up no more than
10 percent of the total weight of the material in the
compost pile. It is better to take newspapers to a
community recycling center.
Other organic materials that can be used to add
nutrients to the pile include blood and bone meal,
livestock manure, prunings from nonwoody plants,
vegetable and flower garden refuse, fruit and vegetable scraps from the kitchen, hay, straw, and lake
plants. Livestock manure and poultry litter can be
added to provide nitrogen. About 100 pounds of
poultry litter provides 1.8 pounds of nitrogen.
Materials to Avoid in a Compost Pile
Some materials may pose a health hazard or create a
nuisance and therefore should not be used to make
compost. Human or pet feces should not be used
because they can transmit disease. Although animal
remains can be safely decomposed in commercial
compostors, wastes such as meat, bones, grease,
whole eggs, and dairy products should be avoided in
home compost piles because they may attract
rodents. Most plant disease organisms and weed
seeds are destroyed during the composting process
because temperatures in the center of the pile reach
150o or 160oF. In most compost piles, however, it is
impossible to mix the contents thoroughly enough to
bring all wastes to the center. Consequently, adding
diseased plants or large amounts of weeds containing
seeds can create problems if the compost is to be
used in the garden.
Citrus rinds; corn cobs, stalks, and husks; palm
fronds; and walnut, pecan, and almond shells break
down very slowly and should be avoided unless they
are shredded. Charcoal also resists decay and will
not decompose in most compost piles. Coal ashes
should not be added because they contain levels of
sulfur and iron that may be toxic to plants. Automotive petroleum products should be taken to recycling
centers, never put into a compost pile.
Although plants that have been treated with
herbicides or pesticides should be avoided for
composting, small amounts of herbicide-treated
plants (for example, grass clippings) can be mixed
into the pile as long as adequate time is allowed for
thorough decomposition. Ideally, clippings from
lawns recently treated with herbicides should be left
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Table 1. Persistence of Herbicides in Soil
Common
Name
Trade Name
Persistence
in Soil (months)
Benefin
Balan, Balfin
4–8
DCPA
Dacthal
4–8
Bensulide
Betasan, Prefar
Glyphosate
Roundup, Kleenup
6–12
Less than 1
2,4-D
(Many formulations)
1–2
MCPP
(Many formulations)
1–3
on the lawn to decompose. Most agrichemicals,
both pesticides and herbicides, degrade at varying
rates. Table 1 lists common chemicals used on
home lawns and gives their degradation rate in soil.
Even if some treated grass clippings are used, the
chemicals they contain should degrade at least as
fast in a properly maintained compost pile as they
do in the soil.
that very little attention is required. Because the
amount of oxygen is limited, however, the process is
slow.
The barrel or drum composter generates compost
rather quickly and provides an easy mechanism for
turning the compost (Figure 1). A barrel of at least
55-gallon capacity with a secure lid is required. Be
sure that the barrel was not used to store toxic
chemicals. Drill six to nine rows of 1/2-inch holes
over the length and a few in the bottom of the barrel
to allow for air circulation and drainage of excess
moisture. Place the barrel upright on blocks to allow
air to circulate below it. Fill the barrel three-fourths
full with organic waste material and add about 1/4 cup
of a fertilizer high in nitrogen (approximately 30
percent nitrogen). Add water until the compost is
moist but not soggy. Every few days, turn the drum
on its side and roll it around the yard to mix and
aerate the compost. The lid can be removed after
Composting Structures
To save space, hasten decomposition, and keep the
yard looking neat, the compost pile can be contained in some sort of structure. If the quantity of
leaves or garden wastes is limited, starting with a
single holding pile constructed as materials are
gathered may be the best approach. This method
also works if minimizing the composting time is not
of great concern.
Composting structures can be made from a
variety of materials and can range from very simple
to complex. The design can be tailored to individual
needs.
Using plastic garbage bags is perhaps the
simplest way to make compost. The bags are easy
to handle and require little maintenance. Large (30to 40-gallon) plastic bags should be filled with
alternating layers of plant wastes, fertilizer, and
lime. About 1 tablespoon of a garden fertilizer with
a high nitrogen content (such as 10-10-10) should
be used in each bag. Lime (1 cup per bag) helps
counteract the extra acidity caused by anaerobic
composting. After the bags have been filled, about
a quart of water should be added and the bags
closed tightly. Set them aside for six months to a
year. The bags can be in a basement or heated
garage to hasten decomposition during winter
months. No turning is required and no water need
be added after the bags have been closed. The
main advantage of composting in garbage bags is
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Figure 1. The barrel or drum composter.
turning to allow for air penetration. The compost
should be ready in two to four months. The barrel
composter is an excellent choice for the city dweller
with a relatively small yard.
For larger quantities of organic waste, bins are
the most practical composting structure. A circular
bin can be made from a length of closely spaced
woven-wire fencing held together with chain snaps
(Figure 2). The bin should be about 3 to 5 feet in
Figure 2. A cylindrical wire bin.
diameter and at least 4 feet high. A stake may be
driven in the middle of the bin before adding material
to help maintain the shape of the pile and to facilitate
adding water. With this design, it is easiest to turn
the composting material by simply unsnapping the
wire, moving the wire cylinder a few feet, and
turning the compost back into it.
A very efficient and durable structure for fast
composting is a three-chambered bin (Figure 3). It
holds a considerable amount of compost and allows
good air circulation. The three-chambered bin works
on the assembly line principle. Three batches of
compost are in varying stages of decomposition at all
times. The composting process is started in the first
bin; waste material is placed in the bin and allowed to
heat for three to five days. Then this material is
turned into the middle bin for another four to seven
days while a new batch of material is started in the
first bin. Finally, the material in the middle bin is
turned into the last bin as finished or nearly finished
compost. The material in the first bin is turned into
the second bin, and new material is once again placed
in the first bin.
To make this structure, it is best to use rotresistant wood such as redwood, salt-treated wood,
wood treated with an environmentally safe preservative, or a combination of treated wood posts and
metal posts. Unless the wood is treated or rot
resistant, it will decompose within a few years. Each
bin should be at least 3 to 5 feet in each dimension
so that it will hold enough volume to compost
properly. Using removable slats in the front of each
bin provides easy access to the contents when they
must be turned.
Many other structures can be used for composting. No one structure is best, and you may want
to invent your own. For a more thorough description
of different structures, see The Complete Book of
Composting, by J. I. Rodale (Rodale Books, Inc.,
Emmaus, PA, 1971.) If you prefer not to build a
structure, you may wish to purchase one of the
commercial composting units available through local
garden stores or mail-order catalogs. Most of these
are similar to the barrel composter described previously and are intended for the city dweller who
wants an easy way to make small amounts of
compost quickly.
Figure 3. A three-chambered bin.
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Location
The compost pile should be located near the place
where the compost will be used. It should also be
placed where it will not offend neighbors or interfere
with activities in the yard. Composting is best done
in a location screened from your view and that of
neighbors. Good locations for the pile are near the
garden or in a service area. Do not locate the
compost pile near a well or on a slope that drains to
surface water, such as a stream or a pond. Locating
the pile too close to trees may also create problems,
as roots may grow into the bottom of the pile,
making turning and handling the compost difficult.
The pile will do best where it is protected from
drying winds and is in partial sunlight to help provide
heat. The more wind and sun the pile is exposed to,
the more water it will need.
Preparing the Compost Pile
When a compost pile is started, materials should be
added in layers to ensure proper mixing. An example of the layering process is illustrated in Figure
4. Organic wastes such as leaves, grass clippings,
and plant trimmings are put down in a layer 8 to 10
inches deep. Coarser materials will decompose
faster if placed in the bottom layer. This layer
should be watered until moist but not soggy. A
nitrogen source should be placed on top of this
Figure 4. Compost pile ingredients.
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layer. Use 1 to 2 inches of livestock manure or a
nitrogen fertilizer such as ammonium nitrate or
ammonium sulfate at a rate of 1/3 cup for every 25
square feet of surface area. If these nitrogen
sources are not available, 1 cup of 10-10-10
fertilizer per 25 square feet of surface area will
suffice. Do not use fertilizer that contains any
herbicide or pesticide.
A 1-inch layer of soil or completed compost can
be applied on top of the fertilizer layer. One reason
for adding soil is to ensure that the pile is inoculated
with decomposing microbes. The use of soil in a
compost pile is optional, however. In most cases,
organic yard wastes such as grass clippings or
leaves contain enough microorganisms on the
surface to cause decomposition. Studies have
shown that there is no advantage in purchasing a
compost starter or inoculum. Microbes multiply as
rapidly from the soil or from added organic wastes
as from the inoculum. The microbes already in the
soil and on organic materials are just as efficient in
decomposing the waste as those provided by the
commercial inoculum. However, one way to
ensure that activator microbes are present in the
new compost is to mix in some old compost as the
pile is prepared. Adding soil does help reduce
leaching of mineral nutrients such as potassium
released during decomposition. Repeat the sequence of adding organic waste, fertilizer, and soil
or old compost (optional) until the pile is completed,
remembering to water each section.
If only tree leaves are to be
composted, layering is not
necessary. Fallen leaves can
be added as they are collected.
The leaves should be moistened if they are dry. Since
dead leaves lack adequate
nitrogen for rapid decomposition, a high-nitrogen fertilizer
(10 to 30 percent) should be
added to hasten breakdown.
Approximately 5 ounces (about
1
/2 cup) of 10 percent nitrogen
fertilizer should be added for
every 20 gallons of handcompressed leaves.
The carbon-to-nitrogen (C/
N) ratio determines how long
decomposition takes. An initial
C/N ratio of about 20 or 30 to
1 is needed for rapid composting. If the initial C/N ratio
is above 50, the process will be
Table 2. Approximate Nitrogen
Concentration and Carbon-to-Nitrogen
(C/N) Ratio of Compost Materials
Material
Grass clippings
Leaves
Nitrogen
(% dry weight)
2.15
0.5–1.0
C/N ratio
20
40–80
Generally, the compost from a well-managed pile
made up of shredded material under warm conditions will be ready in about two to four months.
Piles prepared in the late fall will not be ready for use
the following spring because the weather is not warm
enough to maintain proper decomposing temperatures inside the pile. A pile left unattended or made
up of material that has not been shredded may take
more than a year to decompose. When the compost
is finished, the pile will be about half its original size
and will have an earthy smell to it.
Sawdust
0.11
511
Wood (pine)
0.07
723
Fruit wastes
1.52
35
Paper
0.25
170
Table scraps
none
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Use of Compost to Improve Soil
1.0
20
Compost is used as an organic amendment to
improve the physical, chemical, and biological
properties of soils. The compost adds air space to the
soil, and incorporating it alleviates compacted
conditions. Adding compost increases the moistureholding capacity of sandy soils, reducing drought
damage to plants. When added to heavy clay soils,
compost improves drainage and aeration. (Note,
however, that adding compost cannot solve drainage
problems that result from poor surface contours or
subsurface conditions. Such problems often must be
solved by regrading, berming, or installing drainage
tiles.)
All of these changes create a better environment
for root growth. Adding compost increases the ability
of the soil to hold and release essential nutrients. The
activity of earthworms and soil microorganisms
beneficial to plant growth is also promoted. Other
benefits include improved seed emergence and water
infiltration as a result of reduced soil crusting.
Amending soils with compost may also reduce the
incidence of damping off disease and root rots. The
microflora present in compost compete with disease
microbes for the sugars and nutrients secreted from
plant roots, preventing these pathogens from growing
and keeping them inactive.
Over time, yearly additions of compost will create
desirable soil structure, making the soil much easier
to work. To improve the physical properties of the
soil, incorporate 1 to 2 inches of well-decomposed
compost into the top 6 to 8 inches of soil.
Though compost does enrich the soil, it releases
nutrients slowly and often does not contain enough
nutrients to supply all the needs of growing plants.
Therefore, it is still important to conduct soil tests
and fertilize your lawns and gardens accordingly.
For more information on soil testing and composting,
contact your county Extension Service agent.
Livestock manure
considerably slower. The C/N ratio of common
organic yard wastes is given in Table 2. Materials
can be blended and mixed to achieve an initial C/
N ratio of 25 to 30. Over time, the C/N ratio will
generally decrease.
Maintaining the Compost Pile
To prevent odors and hasten decomposition, the
pile must be turned occasionally. Turning also
exposes seeds, insect larvae, and pathogens to
lethal temperatures inside the pile. The pile may
be turned by inverting segments of the compost
or by shifting the pile into another bin. The pile
should be kept moist but not waterlogged. Odors
may arise either from adding excessive amounts
of wet plant materials, such as fruits or grass
clippings, or from overwatering. A properly
mixed and adequately turned compost pile does
not produce objectionable odors. The middle of
an actively decomposing pile reaches temperatures of 150° to 160°F. If the pile does not heat
sufficiently, it may be too small, there may not
be enough nitrogen or oxygen, or it may be too
wet or too dry. The pile should be turned when
the center begins to feel cool to the touch.
Turning the pile introduces oxygen and
undecomposed material into the center, regenerating the heating process. Composting is essentially
complete when mixing no longer produces heat in
the pile.
Small amounts of fresh materials may be
added if the pile is turned occasionally. Vegetable
wastes should be buried inside the pile to avoid
attracting rodents. If enough material is available,
it is best to make a new pile instead of combining
new material with old compost.
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Feed the landscape
...not the landfill.
Prepared by
Larry Bass, Extension Horticulture Specialist
T. E. Bilderback, Extension Specialist, Nursery Crops
M. A. Powell, Extension Horticulture Specialist
Consulting Technical Writer: Teri Houck
Graphic Artist: Karl E. Larson
This publication was supported in part by the Office of Solid Waste Reduction,
North Carolina Department of Environment, Health, and Natural Resources.
Printed on recycled paper.
Published by
NORTH CAROLINA COOPERATIVE EXTENSION SERVICE
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all
people regardless of race, color, national origin, sex, age, or handicap. North Carolina State University, North Carolina A&T State University,
U.S. Department of Agriculture, and local governments cooperating.
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7/92—10M—TAH—220374
AG-467